This invention relates generally to the field of electroplating, and more particularly to an electroplating system used in the interconnection of electronic devices.
A large variety of articles are made onto which high quality precious and non-precious metals are electroplated for protective coatings. Particularly well known are jewelry articles where metal coatings improve appearance. In many other applications, metal coatings are used for surface protection to prevent corrosion and/or serve as a diffusion barrier, as for example in the fabrication of electronic devices. In other applications of electrical or electronic devices, metal films are used as electrical contact surfaces. In many of these applications, metal films which have high purity, are free of defects, and have controlled thickness and hardness are required. These quality levels and the necessary manufacturing controls contribute to a significant increase in the cost of such articles.
Integrated circuit devices, having an integrated circuit chip and a lead frame which are sealed within a protective enclosure find wide use in products, among which are consumer electronics, computers, automobiles, telecommunications and military applications. A means to electrically interconnect an integrated circuit chip to circuitry external to the device frequently takes the form of a lead frame. The lead frame is formed from a highly electrically conductive material, such as copper or copper alloys, which are stamped or etched into a plurality of leads and a central area in which the integrated circuit chip is attached. The chip is electrically connected to the leads, usually by wire bonding and the device is encapsulated to provide mechanical and environmental protection.
The lead frames are coated partially or completely with thin films of metals compatible with bonding techniques such as wire bonds or solder, and which are deposited by electroplating. The surface finish of the lead frame plays and important role in the ability to attain a reproducible manufacturing process for connecting the chip. In turn, the required surface finish contributes to lead frames being the most costly piece part used in the assembly of plastic encapsulated integrated circuits.
In plating applications where it is feasible, there are cost advantages to plating the lead frames as a continuous part, as opposed to individual pieces. For relatively thin articles, use of a reel to reel handling mechanism allows continuous plating of long pieces with a minimum number of interventions and consequently fewer opportunities for contamination of the plating baths. In particular, this technique has been applied to the manufacture of thin metal coatings, such as nickel, palladium and silver on lead frames for interconnecting integrated circuits.
While automation techniques, such as continuous reel to reel plating of lead frames do help to reduce costs, expenses associated with plating also involves productivity of the plating lines, cost and maintenance of equipment, cost of plating chemicals and high purity water, and of increasing concern, the cost of recovery or waste treatment associated with plating chemicals.
One very important aspect of the continuous plating line is chemicals dragged from the primary plating baths; included are avoidance of cross contamination of baths, loss material, in particular precious metals, and recovery and disposal impacts both on cost and on the environment, and
Methods to efficiently process the chemicals and costly metals dragged out from primary plating process baths is of ongoing interest to the industry.
In accordance with the present invention, there is provided an efficient system and method for minimizing the loss of chemicals dragged out of the processing baths during the plating, including precious metals. The integrated system further drastically reduces the rinse water requirements, significantly minimizes waste treatments, and for reduces plating line maintenance time.
It is an object of the invention to provide an enhanced gradient dragout system which conserves plating and other chemical process solutions by heating the first dragout station, concentrating and maintaining a constant concentration of dragout chemicals in the first station, and returning the solution to the process bath, thereby virtually eliminating the loss of plating chemicals due to being dragged out. This is of particular importance to precious metals or toxic materials requiring recovery, in addition to disposal.
Another object of the invention is to provide an integrated dragout system and process which minimizes deionized water consumption by adding clean water only at the final station, and using a constant level system driven by the evaporation in the first dragout station to maintain solution levels in each of the dragout rinse stations.
Yet another object is to provide a system and process which reduces the need for waste treatment by maintaining the final stations at a very low level of contamination, thereby eliminating the need to empty and treat the solution. Further, the dragout chemicals concentrated in the first station are reused.
Another object of the invention is to provide a system with reduced maintenance owing to the infrequent need to change dragout rinse solutions.
Still another object of the invention is to provide a more effective rinse by heating a rinse tank.
And yet another object of the invention is to provide a process having a relatively high speed and throughput.
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate understanding of the invention.